Understanding Binary Numbers, Decimal Conversion, and File I/O in Computer Science

1. CMSC201 Computer Science I for MajorsLecture 20 – Binary (and File I/O)

2. Last Class We Covered • File I/O • How to open a file • For reading or writing • How to read from a file • How to write to a file • How to close a file

3. Any Questions from Last Time?

4. Today’s Objectives • To understand how data is represented and stored in memory • Binary numbers • Converting • Binary to Decimal • Decimal to Binary • To review what we learned about file I/O

5. “Bridge Course” • We are offering CMSC 291 again this summer • Course for CMSC/CMPE students who earn a “C” instead of the “B” required for their major • Grade must be result of a single poor score (e.g., did badly on the midterm or a project) • Won’t change CMSC 201 grade, but will alloweligible students to take CMSC 202 in Fall 18 • An announcement was made on Blackboard containing all of the details last week

6. Binary Numbers

7. Binary Numbers • Computers store all information (code, text, images, sound,) as a binary representation • “Binary” means only two parts: 0 and 1 • Specific formats for each file help the computer know what type of item/object it is • But why use binary?

8. Decimal vs Binary • Why do we use decimal numbers? • Ones, tens, hundreds, thousands, etc. • But computers don’t have fingers… • What do they have instead? • They only have two states: “on” and “off”

9. Decimal Example • How do we represent a number like 50,932? 2 x 100 = 2 3 x 101 = 30 9 x 102 = 900 0 x 103 = 0000 5 x 104 = 50000 ------ Total: 50932 ten thousands thousands hundreds tens ones 0 9 3 2 5 104 103 102 101 100 Decimal uses 10 digits, so…

10. Another Decimal Example 60000+7000+400+90+3 = 67493

11. Binary Example • Let’s do the same with 10110 in binary 0 x 20 = 0 1 x 21 = 2 1 x 22 = 4 0 x 23 = 0 1 x 24 = 16 -- Total: 22 sixteens eights fours twos ones 0 1 1 0 1 24 23 22 21 20 Binary uses 2 digits, so our base isn’t 10, but…

12. Binary to Decimal Conversion • Step 1: Draw Conversion Box • Step 2: Enter Binary Number • Step 3: Multiply • Step 4: Add 128 + 0 + 0 + 0 + 8 + 4 + 0 + 1 = 141

13. Exercise: Converting From Binary • What are the decimals equivalents of… 101 1111 100000 101010 0010 1010 1000 0000 Longer binary numbers are often broken into blocks of four digits for the sake of readability

14. Exercise: Converting From Binary • What are the decimals equivalents of… 101 = 4+0+1 = 5 1111 = 8+4+2+1 = 15 100000 = 32+0+0+0+0+0 = 32 101010 = 32+0+8+0+2+0 = 42 0010 1010 = 32+0+8+0+2+0 = 42 1000 0000 = 128+...+0+0 = 128

15. Decimal to Binary Conversion • Step 1: Draw Conversion Box • Step 2: Compare decimal to highest binary value • Step 3: If binary value is smaller, put a 1 there and subtract the value from the decimal number • Step 4: Repeat until 0 Convert 163 to binary 163-128 = 35 35-32 = 3 3-2=1 1-1=0

16. Converting to Binary • What are the binary equivalents of… 9 27 68 216 255

17. Converting to Binary • What are the binary equivalents of… 9 = 1001 (or 8+1) 27 = 0001 1011 (or 16+8+2+1) 68 = 0100 0100 (or 64+4) 216 = 1101 1000 (or 128+64+16+8) 255 = 1111 1111 (or 128+64+32+16+8+4+2+1)

18. Binary Tips and Tricks • Some “sanity checking” rules for conversions: • Binary can only be 1 or 0 • If you get “2” of something, it’s wrong • Odd numbers must have a 1 in the ones column • Why? (And what’s the rule for even numbers?) • Each column’s value is the sum of all of the previous columns (to the right) plus one • In decimal, what column comes after 999?

19. File Input and Output(Review)

20. Quick Review • Write the lines of code for the tasks below • Open the file “goodDogs.txt” • Read the file in (however you want), and print out each dog’s name in the sentence “X is a good dog” • Finish using the file (what do you need to do?) goodDogs.txt Thor,Corgi Coco,Chocolate Lab Beethoven,St. Bernard

21. Exercise: Jabberwocky • Write a program that goes through a file and reports the longest line in the file Example Input File: carroll.txt Beware the Jabberwock, my son, the jaws that bite, the claws that catch, Beware the JubJub bird and shun the frumiousbandersnatch. Example Output: >>>longest.py longest line = 42 characters the jaws that bite, the claws that catch,

22. Jabberwocky Solution Pseudocode inside main: open the file "carroll.txt" (for reading) create a variable to store the "longest" line # we'll refer to this variable as "record" # what should this variable be initialized to? for each line of the input if the current line is longer than the record update the record to the current line print the length of the longest line print the longest line call main

23. Jabberwocky Solution Code defmain(): inputFile= open("carroll.txt") longest = "" lines = inputFile.readlines() foriinrange(len(lines)): iflen(lines[i]) > len(longest): longest = lines[i] print("Longest line =", len(longest)) print(longest) main()

24. Jabberwocky Solution Walkthrough Beware the Jabberwock, my son, the jaws that bite, the claws that catch, Beware the JubJub bird and shun the frumiousbandersnatch. line = line = "Beware the Jabberwock, my son," longest = "" longest = "Beware the Jabberwock, my son," len(line) > len(longest) for i in range(len(lines)): if len(lines[i]) > len(longest) longest = lines[i] 31 > 0 

25. Jabberwocky Solution Walkthrough Beware the Jabberwock, my son, the jaws that bite, the claws that catch, Beware the JubJub bird and shun the frumiousbandersnatch. line = line = "the jaws that bite, the claws that catch," longest = "" longest = "Beware the Jabberwock, my son," longest = "the jaws that bite, the claws that catch," len(line) > len(longest) for i in range(len(lines)): if len(lines[i]) > len(longest) longest = lines[i] 42 > 31 

26. Jabberwocky Solution Walkthrough Beware the Jabberwock, my son, the jaws that bite, the claws that catch, Beware the JubJub bird and shun the frumiousbandersnatch. line = • line = "Beware the JubJub bird and shun" longest = "" longest = "Beware the Jabberwock, my son," longest = "the jaws that bite, the claws that catch," len(line) > len(longest) for i in range(len(lines)): if len(lines[i]) > len(longest) longest = lines[i] 32 > 42 

27. Jabberwocky Solution Walkthrough Beware the Jabberwock, my son, the jaws that bite, the claws that catch, Beware the JubJub bird and shun the frumiousbandersnatch. line = • line = "the frumiousbandersnatch." longest = "" longest = "Beware the Jabberwock, my son," longest = "the jaws that bite, the claws that catch," len(line) > len(longest) for i in range(len(lines)): if len(lines[i]) > len(longest) longest = lines[i] 27 > 42 

28. Daily CS History • Katherine Johnson • Worked as a NASA “computer” • Calculated trajectories, launch windows, and return paths forflights in Project Mercury • Plotted Alan Shepard’s 1961 journey to space (first American) • Also examined black box data from crashed air planes • Graduated college at age 18

29. Announcements • Homework 6 is available on Blackboard • Parts 4 and 5 do not require recursion • Homework is due on Friday, April 27th • Final exam is when? • Friday, May 18th from 6 to 8 PM • If you can’t take the exam then, you need to let Dr. Gibson know via email by Wednesday @ 9 PM

30. Image Sources • Katherine Johnson: • https://commons.wikimedia.org/wiki/File:Katherine_Johnson_at_NASA,_in_1966.jpg